The present invention relates generally to a wide-angle, high-zoom-ratio zoom lens, and more specifically to a compact, inexpensive zoom lens for use with image pickup systems or the like, which has a wide-angle arrangement as represented by a diagonal angle of view of 70° or greater at the wide-angle end, a high zoom ratio of 5 to 10 and high image-formation capabilities and comprises a reduced number of lens components.
For instance, patent publication 1 listed below discloses a zoom lens having a zoom ratio of about 20 and an angle of view of 60° or greater at the wide-angle end and comprising a first lens group that remains stationary and has positive power, a second lens group having negative power, a third lens group having positive power, a fourth lens group having negative power and a fifth lens group that remains stationary and has positive power.
Patent publication 2, listed below, discloses a zoom lens having a zoom ratio of about 20 and an angle of view of 60° or greater at the wide-angle end and comprising a first lens group having positive power, a second lens group having negative power, a third lens group having positive power, a fourth lens group having negative power and a fifth lens group having positive power.
Patent publication 3, listed below, discloses a zoom lens comprising a first lens group having positive power, a second lens group having negative power, a third lens group having positive power and a fourth lens group having positive power.    Patent Publication 1
JP-A 08-5913    Patent Publication 2
JP-A 08-190051    Patent Publication 3
JP-A 2001-194590
In the zoom lenses set forth in patent publications 1 and 2, however, the first lens group remains fixed and the front lens has a large diameter; no wide-angle arrangement is achievable while the diameter of the front lens is kept small. Since the second lens group is a unit system, it is difficult to attain aberrational balances between the wide-angle end and the telephoto end. It is also difficult to make correction for aberrations because the second lens group has too strong power.
The zoom lens of patent publication 3 requires a lens component having negative power strong enough to flip up light rays thereby making emergent light telecentric. However, this negative lens component having strong power is located within the third lens group. On the other hand, the third lens group has a zooming function, and so has increased power with an increased amount of movement for zooming. The location of the negative lens component having strong power within the third lens group incurs large fluctuations of astigmatism and coma. To correct the zoom lens for such aberration fluctuations, so many lens components are needed, resulting in increased costs.